1. Technical Field of the Invention
The present invention relates to a stationary blade of a gas turbine and in particular to a structure and a method for inserting inserts into hollow openings provided in the stationary blade of a gas turbine for cooling same.
2. Description of the Related Art
The internal portion of a stationary blade of a conventional gas turbine is provided with a front hollow opening 2, an intermediate hollow opening 3 and a rear hollow opening 4, as is shown in FIG. 4. Inserted into the hollow openings 2, 3 and 4 are a front insert 5, an intermediate insert 6 and a rear insert 7, respectively, each of which is formed as a hollow member corresponding to the hollow opening. The inserts 5, 6 and 7 are each formed of a thin plate provided with a number of cooling-air ejecting apertures 8 each having a diameter of 0.1 to 0.5 mm.
In the gas-turbine stationary blade 1 of the structure mentioned above, cooling air is supplied to the hollow portions of the inserts 5, 6 and 7 during driving of the gas turbine, wherein the cooling air passes through the cooling-air ejecting apertures 8 formed in the inserts 5, 6 and 7 to impinge onto the wall surfaces of the hollow openings 2, 3 and 4 formed in the internal portion of the gas-turbine stationary blade 1 to thereby cool the gas-turbine stationary blade 1 from the inside.
When cooling the gas-turbine stationary blade 1 from the inside in this manner, the cooling-air ejecting apertures 8 formed in the inserts 5, 6 and 7 function as orifices because of the small diameters thereof to thereby constrict the flow of the cooling air. Thus, the cooling of the gas-turbine stationary blade 1 with the cooling air can be performed efficiently and effectively.
In the conventional gas-turbine stationary blade, the wall surfaces of each of the hollow openings 2, 3 and 4 are provided with three or more projecting portions 20, as are shown in FIG. 5, wherein each of the inserts 5, 6 and 7 is held by the projecting portions 20 to allow the cooling air to flow through the space defined between the wall surface and the insert. The inserts 5, 6 and 7 have fitting structures such that they fit snugly with the projecting portions 20. Moreover, the projecting portions 20 are finished by machining so as to conform to the outer dimensions of the inserts 5, 6 and 7 so that the inserts can be reliably held.
Gas turbines have hereinbefore been operated with a combustion gas having a temperature of 1500.degree. C. or less. Recently, however, efforts have been made to develop a gas turbine which can be operated with a combustion gas having a temperature of 1500.degree. C. so as to enhance the efficiency of the gas turbine. In order to allow a 1500.degree. C. class gas turbine to be employed in practical applications, the inserts have to be fabricated using a plate of Hastelloy with a thickness of 0.5 mm.
However, when the same fitting structures as the conventional ones, for holding the individual inserts 5, 6 and 7 within the hollow openings 2, 3 and 4 are adopted it is difficult to form the projection portions 20 by machining, thus making it difficult to properly position the inserts. Consequently, some portions of the gas-turbine stationary blade 1 may not be able to be sufficiently cooled to withstand the high temperature 1500.degree. C. combustion gas.